Field of Invention
The invention relates to an axial flow fan and a control method thereof. In particularly, the invention relates to an axial flow fan with forward/reverse rotation characteristics, and a control method thereof.
Related Art
Currently axial flow fans are used for variety of purposes, such as the fan for cooling an electronic device and the outdoor unit for an air conditioner, and the effects of high efficiencies and low noises have been obtained through research and development with various techniques. Please refer to FIGS. 1A and 1B, wherein FIG. 1A is a top view of the base of a conventional axial flow fan 1, and FIG. 1B is a partially enlarged view of the hub 15 and one of the blades 13 in FIG. 1A viewing from the side of the axial flow fan 1 having connecting members 14. The axial flow fan 1 has a fan frame 11, a base 12, a plurality of blades 13, a plurality of connecting member 14, and a hub 15. The blades 13 have outer peripheral end 16 away from the hub 15, and the bottom of the outer peripheral end 16 has an end point 17.
FIG. 2 is a graph of the characteristics of the forward and reverse rotations of the axial flow fan 1. In FIG. 2, the horizontal axis represents the flow quantity of the axial flow fan in cubic feet per minute (CFM), and the vertical axis represents the static pressure of the axial flow fan in millimeter aqua (mmAq). From the graph of FIG. 2, it can be easily observed that the characteristic curve L1 of the axial flow fan 1 during forward rotations is quite different from the characteristic curve L2 during reverse rotation. Since the axial flow fans are mostly used under the status of rotating forwardly, the axial flow fans are designed with the consideration of optimizing the characteristics and efficiency of the forward rotations of the axial flow fan. Therefore, without considering the use of the axial flow fan for reverse rotations, the designs of the shapes of the blades 13 and the connecting members 14 of the conventional axial flow fan 1 (as shown in FIG. 1B) are focused on the presumption of using the axial flow fan for forward rotations, which results in that the characteristics of the forward rotations of the axial flow fan are better than the characteristics of the reverse rotations of the axial flow fan.
However, in different applications where it is necessary to make the characteristics of the forward rotations be close to the characteristics of the reverse rotations, the conventional axial flow fan is not suitable. For such applications the construction of the axial flow fan must be re-designed to consider the characteristics of both forward and reverse rotations. Therefore, it is an important subject to provide an axial flow fan with similar forward and reverse rotation characteristics and a control method thereof.